The characteristics of dissolved organic matter (DOM) and its relationships with other environmental factors are beneficial for comprehending water pollution in watersheds. This study aimed to improve our understanding of the association of DOM with water quality by connecting the spectroscopic characteristics of DOM with land cover and land use (LCLU). Clustering the tributaries of the Miho upstream watershed according to LCLU resulted in Clusters 1 and 2 having a large proportion of farmland and a large forest area, respectively. Various fluorescence indices derived from fluorescence excitation-emission matrix spectra revealed that livestock effluent resulted in the enrichment of autochthonous organic matter of algal or microbial origin in catchment areas with a high proportion of farmland. Furthermore, to analyze water quality changes according to the land-use characteristics, the water quality and spectroscopic characteristics of DOM were utilized based on the period of farmland use. Further correlation analysis indicated a high correlation between the fluorescence index (FI) in Cluster 1 and organic matter parameters and nitrogenous pollution (Total nitrogen (TN), Dissolved total nitrogen (DTN) and Nitrate nitrogen (NO₃-N)) (planting season, r = 0.991, post-planting season, r = 0.971). This suggests that the FI can be used as a surrogate to estimate the degree of water pollution in watersheds largely affected by land uses related to agricultural activity and the livestock industries.

中文翻译：

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以农业为主的流域河流水质与溶解有机物荧光特性密切相关

溶解有机物（DOM）的特征及其与其他环境因素的关系有助于理解流域水污染。本研究旨在通过将 DOM 的光谱特征与土地覆盖和土地利用 (LCLU) 联系起来，提高我们对 DOM 与水质关系的理解。根据 LCLU 对 Miho 上游流域的支流进行聚类，结果聚类 1 和聚类 2 分别具有较大比例的农田和较大的森林面积。来自荧光激发-发射矩阵光谱的各种荧光指数表明，在农田比例较高的集水区，牲畜流出物导致藻类或微生物来源的本土有机物富集。此外，为根据土地利用特征分析水质变化，根据耕地利用时期，利用DOM的水质和光谱特征。进一步的相关性分析表明，Cluster 1 中的荧光指数（FI）与有机质参数和含氮污染（总氮（TN）、溶解总氮（DTN）和硝酸盐氮（NO₃ -N))（种植季节，r = 0.991，种植后季节，r = 0.971）。这表明 FI 可用作估算流域水污染程度的替代指标，该流域主要受与农业活动和畜牧业相关的土地利用影响。